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Saturday, 18 August 2012

Orchid Foes--and Friends (a follow-up)

A daily survey of the orchid collection provided this little vignette.

The Orchid Weevil, Orchidophilus aterrimus (Waterhouse) was about to be attacked by a Jumping Spider.

Ah, I thought what a great thing. Biological control in action. But alas, it was not to be.

But after a fraction of a second, the spider released the prey and moved away. Several bouts were observed in just a few minutes time and then the spider hopped away. Note the weevil is firmly attached to the substrate. So that got me to thinking what makes a "successful" pest.

In this instance, perhaps, the spider could not penetrate the tough exoskeleton of the weevil. Entomologists will tell you difficult it is to pin a large weevil. A #5 stainless steel pin often will not penetrate the exoskeleton of the specimen. If this is working in this example, it is surprising the spider's chelicerae could not find a membrane or other soft point to penetrate. But after several attempts it could not.

And, perhaps, the weevil excreted a chemical of some sort that discouraged the spider. But if this were the case, the spider would not have made repeated attempts at capture.

The weevil stayed "glued" in the same position for 15 minutes until I decided it was time for the alcohol treatment. The spider wandered off. There are not many food sources in the shadehouse so I hope the spider will sharpen its chelicerae for the next encounter.

The spider. It is a Jumping Spider, family Salticidae. There is a great spider site on the web dealing with Aussie spiders. But I cannot reliably identify the genus of this little spider so will not guess. Perhaps, a reader will be able to put a name on it.

8 comments:

Gosh David.I was cheering for the Weevil, but saw you were clearly cheering for the Jumping Spider.That surprised me, till I remembered you are fond of your Orchid collection too (as well as insects and spiders).That Spider's vision must be amazing as it seems to have eyes on all corners of its head.Denis

Hi DenisYes, the spider seems to have no problem seeing. But you would think that he (she) would be able to find a membrane to penetrate, but no. There are a couple of salticid species in the shadehouse. i am thankful that they must get the odd moth that gets in there, hopefully before it lays any eggs.D

I have just witnessed a large ant attacking a tiny black weevil just like yours. The ant left the weevil alone shortly after realizing the weevil is too hard for it too bite. The weevil is smaller than the ant's head and yet the ant is no match for it. This is another proof to support what you said about weevils being the ultimate pest (I guess that is what you meant).

About Me

David and family moved to Kuranda, Queensland in 2002, following retirement from CSIRO Canberra, Australia. David, Barbara and an assortment of wildlife live in a rainforest setting. It is their first experience living in the tropics.
David's major interest is Entomology. He continues research in the Orthopteroid insects and is keenly interested in the biology of the rainforest.
This blog is a narrative of observations made in and around Kuranda.
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